Reconsider the need for publishing Vagrant baseboxes

After a nice discussion with Ximin, anonym and others last week, our conclusion was that we should simply not publish nor host any Vagrant basebox at all, but instead make it trivial to create your own.

Advantages:

• one less binary blob used as input of the build => huge increase of the value of reproducible ISO builds
• with the basebox defined as code, if I need a new basebox for some new branch I’ll just have to change code, and not manually build + upload a basebox to some place
• no need to do #11982 (closed) + the repetitive work it commits us to do forever
• less infra development work
• less upload bandwidth required on our servers

Drawbacks:

• some more build system coding to do, to automate the basebox creation process
• non-Debian build hosts might be a problem, e.g. if some tools used to create baseboxes are not readily available on other distros
• more storage needed on isobuilders (to build the baseboxes)

If we decide to go this way, it changes quite a lot what’s on anonym’s and bertagaz’ plate, so let’s try to reach a prompt conclusion.

Feature Branch: feature/12409-improved-vagrant-base-box-versioning

Parent Task: #5630 (closed)

Original created by @intrigeri on 12409 (Redmine)